Various photopolymerizable composition comprising both ethylenically unsaturated polymerizable compounds and polymerizable epoxides are known in the art. Ethylenically unsaturated compounds, such as acrylate derivatives, can be polymerized by exposure to radiation, typically ultraviolet light, in the presence of a photoinitiating system.
Photoinitiators can be either cleavage type or abstraction type initiators. Typically, an abstraction type photoinitiating system includes (1) a compound capable of initiating polymerization of the ethylenically unsaturated compound upon exposure to radiation (a “photoinitiator”), and optionally (2) a co-initiator or synergist, that is, a molecule that serves as a hydrogen atom donor. Useful co-initiators or synergists are typically alcohols, tertiary amines, amides, or ethers that have labile hydrogen atoms attached to a carbon adjacent to a heteroatom. Currently, commercially available photoinitiators include benzophenones and derivatives thereof and thioxanthone derivatives.
Epoxies are generally polymerized by exposure to radiation such as ultraviolet light in the presence of an onium salt photoinitiating system. It is well known that various onium salts, upon exposure to radiation, are capable of forming a Bronsted acid, and that the Bronsted acid thus formed can cure a wide variety of materials including epoxies. See, for example, UV Curing: Science and Technology, edited by S. Peter Pappas and published (1978) by Technology Marketing Corporation, 64 Westover Road (Stamford, Conn. 06902) and U.S. Pat. No. 4,273,668 (Crivello). Acid generating onium salt photoinitiators are well known in the art and include, for example, diaryliodonium and triarylsulfonium salts. Useful counter anions for onium salts include complex metal halides such as tetrafluoroborate, hexafluoroantimonate, trifluoromethanesulfonate, hexafluoroarsenate, and hexafluorophosphate.
Polymer composites comprising metal or metal oxide nanoparticles have been developed and tested for various applications due to their potential for a variety of unique electrical, thermal, mechanical, or optical properties.
Photocurable polymer composites comprising metal or metal oxide nanoparticles are also known. For example, U.S. Pat. No. 6,417,244 (Wellinghoff et al.) discloses a photopolymerizable composition comprising a combination of monomers selected from a bis-acrylate or bis-methacrylate in combination with metal oxide nanoparticles, which composition is used for dental restoration.
One major problem with the use of onium salts is that they do not absorb radiation out to 400 nm, and commonly must be used in combination with a light-absorbing photosensitizer in order to carry out photoinitiation at wavelengths longer than 300 nm. In addition, it has been found that in presence of certain metal nanoparticles, the absorption spectrum of commercially available sulfonium salts moves to shorter wavelengths.
Thus, it is desired to provide a photopolymerizable composition containing epoxy compounds and metal nanoparticles that can be photocured (photopolymerized) with high efficiency, thereby overcoming the problems noted above.